Hernandez J.A.,Academia de Biotecnologia y Farmacia |
Gomez S.A.,Metropolitan Autonomous University |
Zepeda T.A.,National Autonomous University of Mexico |
Fierro-Gonzalez J.C.,Celaya Institute of Technology |
Fuentes G.A.,Metropolitan Autonomous University
ACS Catalysis | Year: 2015
The activity and deactivation of Au/CeO2 catalysts in the PROX reaction were measured during long-term experiments (TOS = 160 h) by in situ DRS-UV-vis spectroscopy. During the reaction, the support showed a decrease in band gap energy. The activity and selectivity to CO2 were closely linked to the reduction of Aun+ species, the sintering of the reduced Au species, and to changes in the Ce3+/Ce4+ ratio. This ratio increased during long-term PROX experiments, showing a decrement of surface oxygen atoms from the CeO2 phase which participated in the reaction, after which the total oxygen fed to the reaction was wholly consumed. Also, almost all of the Au3+ species initially present in the catalysts were reduced to Au+ and Au0. Results suggest that the activity loss is connected to the fast reduction of Au species and is also linked to changes in the redox properties of ceria, breaking the cycle that provides oxygen to the reaction. Sintering of the Au nanoparticles occurs in a longer time scale. On the other hand, in the case of fresh Au/CeO2 catalysts, the Aun+/Au0 ratio decreased with increasing Au content. This initial ratio affects CO2 selectivity as a function of temperature. © 2015 American Chemical Society.
Gallardo-Alvarado J.,Celaya Institute of Technology
Robotics and Computer-Integrated Manufacturing | Year: 2012
In this work the jerk analysis of a 3-RRPS parallel manipulator to realize six degrees of freedom is approached by means of the theory of screws. The input/output equations of velocity, acceleration and jerk of the moving platform with respect to the fixed platform are obtained systematically by resorting to reciprocal-screw theory. A numerical example is included in order to show the application of the method of kinematic analysis. Furthermore, the numerical results obtained via screw theory are satisfactorily compared with simulations generated with the aid of commercially available software. © 2011 Elsevier Ltd. All rights reserved.
Navarrete-Bolanos J.L.,Celaya Institute of Technology
Engineering in Life Sciences | Year: 2012
Fermented foods and beverages are an intrinsic part of our diet. All over the world, regional quality products are produced by native microorganisms in their natural ecosystems, giving the basis for registering appellations of origin. For wines, premium quality products can be obtained by spontaneous fermentation; its success depends heavily on environmental conditions. Inoculated fermentations with selected pure cultures have been developed as alternative; however, the products obtained have a plain aromatic profile compared to those obtained by successful spontaneous fermentations. Several studies have shown that inoculums of native mixed cultures are able to exalt the peculiarities (aroma, structure, and color) of a wine, and preserve their authenticity and uniqueness; however, reliable methods for native microorganism selection are still limited. Currently, the strain selection criterion is based on their genetic endowment; but, the design of an efficient fermentation process requires also knowledge on physicochemical effectors to maximize the metabolic capacity of the selected strains. This article reviews the guidelines for strain selection, and discusses directions for exploring the use of these microorganisms specifying their operating conditions. The main goal of this work is to present the strategy of how to evolve a spontaneous fermentation to directed fermentation. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Gallardo-Alvarado J.,Celaya Institute of Technology
Journal of Intelligent and Robotic Systems: Theory and Applications | Year: 2014
In this work the hyper-jerk analysis of robot manipulators is addressed by means of the theory of screws. The reduced hyper-jerk state of a rigid body as observed from another body or reference frame is obtained as a six-dimensional vector by applying the concept of helicoidal vector field. Moreover, this contribution demonstrates that the reduced hyper-jerk state of a rigid body can be considered, similar to the velocity state, as a twist about a screw. Furthermore, the reduced hyper-jerk state is systematically obtained in pure screw form. Finally, a case study, which is verified with the aid of commercially available software, that consists of solving the kinematics, up to the hyper-jerk analysis, of a zero-torsion parallel manipulator is included in order to show the application of the method of kinematic analysis. © Springer Science+Business Media Dordrecht 2014.
Gomez-Gualdron D.A.,Texas A&M University |
McKenzie G.D.,Texas A&M University |
Alvarado J.F.J.,Celaya Institute of Technology |
Balbuena P.B.,Texas A&M University
ACS Nano | Year: 2012
Single-walled carbon nanotubes (SCWNTs) have outstanding properties that depend on structural features such as their chirality. Thus, developing a strategy to control chirality during SWCNT synthesis is critical for the exploitation of nanotube-based technologies in fields such as electronics and biomedicine. In response to this need, tuning the nanocatalyst structure has been envisioned as a means to control the nanotube structure. We use reactive classical molecular dynamics to simulate nanotube growth on supported Ni 32, Ni 80, and Ni 160 nanoparticles at various metal/support interaction strengths (E adh). The initial carbon ring formation is shown to correlate to the nanoparticle surface structure, demonstrating the existence of a "template effect" through a dominant occupation of hollow sites. The E adh strength alters the dynamic/structural behavior of the nanoparticle, in turn influencing the interplay between nanotube and nanoparticle structures. For example, the contact region between the nanoparticle surface and the growing nanotube decreases as E adh increases because capillary forces that raise the metal into the nanotube are counteracted by the strong metal/support interaction. The nanoparticle mobility decreases as E adh increases, eliminating a possible inverse template effect but hindering defect annealing in detriment of the nanotube/nanoparticle structural correlation. On the other hand, the contact between the nanoparticle and the nanotube increases with nanoparticle size. However, the heterogeneity of the nanoparticle structure increases with size, reducing the structural correlation. These results suggest that an appropriate combination of nanoparticle size and strength of the catalyst/support interaction may enhance the desired template effect and bias formation of specific nanotube chiralities. © 2011 American Chemical Society.